1. Field of the Invention
The present invention relates to an inkjet printing apparatus and a printing system each using a printing head that ejects ink to perform printing, and a control method for the same system.
2. Description of the Related Art
In general, the inkjet printing apparatus includes a carriage on which a printing head as a printing unit and an ink tank are mounted, a conveying unit that conveys, for example, printing paper as a printing medium, and a control unit for controlling the drive of the carriage and conveying unit. The inkjet printing apparatus moves the carriage on which the printing head is mounted in a direction intersecting a conveying direction of the printing medium. In the course of this movement, a plurality of ink ejection openings of the printing head eject ink. When this movement is completed, the printing medium is conveyed by a predetermined amount. Movement of the printing head and conveyance of the printing medium are alternately repeated to thereby perform printing on the entire printing medium.
In the aforementioned inkjet printing apparatus, there is an important relationship between the printing medium and the amount of ink applied thereto. For example, when a large amount of ink is ejected onto the printing medium such as-platen at one time, swelling occurs, with the result that waving of the printing medium, which is called cockling, is generated. When such cockling is severe, the printing medium and the printing head may come into contact with each other, and thus be fouled.
In order to avoid this problem, it is considered that a distance between a printing surface of the printing medium and the printing head is sufficiently ensured in advance to prevent the printing medium from coming into contact with the printing head even when cockling occurs. However, the inkjet printing apparatus performs printing by ejecting ink while moving the printing head with respect to the printing medium. Thus, when the above distance is too large, the accuracy of dot-landing positions on the printing medium is reduced, making dot-forming positions unstable, which results in a decrease in image quality. For this reason, conversely, it is desirable that the above distance be small in view of improvement of the image quality.
In order to solve the problem of contact between the printing medium and the printing head caused by deflection of the printing medium due to cockling, a configuration is proposed in which a distance between a printing head and a platen for supporting the printing head, the distance being referred as ‘head-to-platen distance’ hereinafter, is adjusted to change a distance between a surface of a printing medium to be printed and the printing head according to duty of an image (see Japanese Patent Laid-Open No. 2002-292856). In this proposal, in the case of a high duty where there is a high possibility that cockling will occur, the head-to-platen distance is set large, while in the case of a low duty where there is a low possibility that cockling will occur, the head-to-platen distance is set small. According to this configuration, it is possible to suppress head rubbing and to achieve higher image quality.
However, in the case of the configuration in Japanese Patent Laid-Open No. 2002-292856, determination processing for determining the content of the image (duty) must be carried out for every image output, so that correspondingly longer time is required for image output. The configuration in Japanese Patent Laid-Open No. 2002-292856 is insufficient for users who put emphasis on speed rather than image quality. Thus, Japanese Patent Laid-Open No. 2002-292856 cannot meet various user needs (for example, emphasis is put on quality or speed, or the like).